Trypanocidal activity of new 1,6-diphenyl-1H-pyrazolo[3,4-b]pyridine derivatives: Synthesis, in vitro and in vivo studies

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Highlights

  • Pyrazolopyridine compounds synthesized and evaluated in vitro/in vivo against T. cruzi.

  • Benzylidene-carbohydrazide and 3-acetyl-2,3-dihydro-1,3,4-oxadiazole derivatives.

  • Two ortho-substituted derivatives showed the best activity profiles.

  • In silico studies suggested a metabolic profile of the most active compounds.

Abstract

Despite the serious public health problems caused by Chagas disease in several countries, the available therapy remains with only two drugs that are poorly active during the chronic phase of the disease in addition to having severe side effects. In search of new trypanocidal agents, herein we describe the synthesis and biological evaluation of eleven new 1,6-diphenyl-1H-pyrazolo[3,4-b]pyridine compounds containing the carbohydrazide or the 2,3-dihydro-1,3,4-oxadiazole moieties. Two of them showed promising in vitro activity against amastigote forms of T. cruzi and were evaluated in vivo in male BALB/c mice infected with T. cruzi Y strain. Our results suggest that the substitution at the C-2 position of the phenyl group connected to the carbohydrazide or to the 2,3-dihydro-1,3,4-oxadiazole moieties plays an important role in the trypanocidal activity of this class of compounds. Moreover, the compound containing the 2,3-dihydro-1,3,4-oxadiazole moiety has demonstrated more favorable structural requirements for in vivo activity than its carbohydrazide analog.

Introduction

Chagas disease remains a neglected tropical disease, although it was discovered more than 100 years ago by Carlos Chagas.1 The protozoan Trypanosoma cruzi was described as the causative agent in 1909,2 which can be transmitted by triatomine insects. The mechanisms of transmission include vectorial transmission, oral, congenital, blood transfusion and organ transplantation.3 Chagas disease can develop into three clinical phases: the acute, indeterminate, and chronic phase. If untreated, the acute phase can develop into a chronic phase.1 The rate of cases that evolve to the chronic symptomatic phase is around 30%.4 Symptomatic patients may usually present morphological and functional changes in organs such as the heart, the colon and the esophagus. The treatment available is based on nitroheterocyclic molecules, Benznidazole and Nifurtimox, which are mainly used to treat patients during the acute phase of the disease as they have little effectiveness in adults with late chronic disease.1

The 1H-pyrazolo[3,4-b]pyridine is one of the potential heterocyclic rings that have been showing wide promising biological applications.5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 In our previous work, we developed 4-(benzylidene-carbohydrazide)-1,6-diphenyl-3-methyl-1H-pyrazolo[3,4-b]pyridine compounds for trypanocidal activity. The N′-(4-hydroxybenzylidene)carbohydrazide derivative (1, Fig. 1) showed in vitro activity against both trypomastigote and amastigote forms of T. cruzi comparable to the benznidazole drug, and a lower cell toxicity profile in mammalian cells.16

Based on the promising biological profile of the hit compound 1, herein, we synthesized new 1,6-diphenyl-1H-pirazolo[3,4-b]pyridine compounds structurally related to 1 and evaluated their trypanocidal activity and cytotoxicity profile.

Section snippets

Chemistry

The reactions were monitored by TLC performed on aluminum sheets precoated with silica gel 60 (HF-254, Merck) to a thickness of 0.25 mm and the chromatograms were viewed under ultraviolet light (254–365 mm). The ultrasound assisted reactions were carried out on an ultrasonic bath Unique UltraCleaner, model 1600 A, at 40 KHz and ultrasonic potency of 135 W. Melting points were determined in a capillary of a Thomas Hoover PC03296 apparatus and are given uncorrected. IR spectra were recorded on a

Synthesis

The new compounds were planned exploring the hydroxyl group in different positions of the benzylidene moiety as well as it’s O-acetyl form, and the bioisosteric concept between carbohydrazide and 2,3-dihydro-1,3,4-oxadiazole moieties.27, 28, 29 In order to investigate the influence of the position of the hydroxyl group at the benzilidene moiety on the trypanocidal activity, we have synthesized four new hydroxybenzilidene-carbohydrazide analogs of 1 (2a-d). We have also synthesized seven new

Conclusions

We synthesized 11 new 1,6-diphenyl-1H-pirazolo[3,4-b]pyridine compounds structurally related to N′-(4-hydroxybenzylidene)carbohydrazide derivative from previous works. The use of glycerol as a reaction medium to produce N′-benzylidene-carbohydrazides (1, 2a-d) proved to be more advantageous than the conventional medium. All compounds tested showed some level of trypanocidal activity in vitro. The comparison between the positions of the substituent group on the phenyl ring indicated that the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like thank for the support of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES-BR) for the JLSR and JCVS fellowships (finance code 001), and the Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ) [E-26/200.930/2017].

The authors would also like to thank the Laboratório Multiusuário de RMN de Líquidos (LABRMN-L) of the Chemistry Institute of UFRJ for its support in the generation of 400 MHz NMR spectra.

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